Beam steering element with built-in detector and system for use thereof

ABSTRACT

An all-optical cross-connect switching system provides optical switching that may reduce processing requirements by three orders of magnitude over conventional techniques by associating at least one optical detector with an optical beam steering element. In one embodiment, a first beam steering element, having a reflective surface in optical association with a first optical fiber array, and a second beam steering element, having a reflective surface in optical association with a second optical fiber array, are optically arranged to direct an optical beam from a first optical fiber in the first optical fiber array to a second optical fiber in the second optical fiber array. The optical detector provides information about a first position of the optical beam on the second beam steering element. Based on this information, the angle of the first beam steering element may be adjusted to cause the optical beam to change to a second position on the second beam steering element.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.11/263,529, filed on Oct. 31, 2005, now abandoned the entire contents ofwhich are incorporated by reference.

BACKGROUND OF THE INVENTION

Increasingly large volumes of information are transferred acrosstelecommunications networks to meet the increasing Internet and businesscommunications demands. High speed communications systems in thetelecommunications networks often employ fiber optic communicationschannels with electronic switches and routers to transfer theincreasingly large volumes of information. However, a combination ofoptical data transmission and electronic switching requires numerousoptical-to-electrical-to-optical conversions. These conversions createsignificant overhead in terms of power consumption, bandwidthlimitations, size of system components, overall system throughput, andlatency. As such, much research has been performed to developall-optical cross-connect switching systems.

In an all-optical cross-connect switching system, optical beams fromtransmitting apertures are connected to corresponding receivingapertures in the switching system by pointing direction, reflection,refraction, diffraction, or combinations thereof. To set-up opticalconnections, conventional optical cross-connect systems generallyutilize secondary optical beams emitted by an array of light emittingdiodes (LEDs) associated with input ports that are used to locate theproper corresponding output or connecting ports, or vice-versa. As partof the set-up process, the connecting ports may employ a detectorcoupled to a fiber receiving the secondary optical beam to detect thesecondary optical beam. However, such a setup requires sophisticatedprocessing, very accurate positioning of the detector components, andsophisticated components. In addition, if the transmission length of theoptical beam is long relative to the size of the receiving aperture, thealgorithm needed to center the optical beam on the receiving aperturebecomes even more complex and/or requires highly sophisticatedprocessing and, thus, more processing time. In an optical cross-connectsystem, these requirements result in undesirable delay in setting-upconnections, higher per-port costs, and lower reliability.

SUMMARY OF THE INVENTION

An all-optical cross-connect switching system provides optical switchingwith significantly reduced processing requirements and cost and withincreased reliability by associating an optical detector with an opticalbeam steering element. In one embodiment, the all-optical cross-connectswitching system includes (i) a first beam steering element having areflective surface in optical association with a first optical fiberarray and (ii) a second beam steering element having a reflectivesurface in optical association with a second optical fiber array. Inthis embodiment, the first and second beam steering elements areoptically arranged to direct an optical beam from a first optical fiberin the first optical fiber array to a second optical fiber in the secondoptical fiber array. Further, in this embodiment, the second beamsteering element includes at least one optical detector that providesinformation about a first position of the optical beam on the secondbeam steering element, which may be an indication of an angle of thefirst beam steering element. Based on this information, the angle of thefirst beam steering element may be adjusted to cause the optical beam tochange to a second position on the second beam steering element.

Other embodiments of the present invention include the optical beamsteering element with built-in detector and a method of manufacturingsame.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a block diagram of an optical cross-connect switching systemthat may employ an embodiment of the present invention;

FIG. 2A is a block diagram of an all-optical cross-connect switchingsystem incorporating an output beam steering element with built-indetector according to an embodiment of the present invention;

FIG. 2B is a block diagram of an all-optical cross-connect switchingsystem incorporating the output beam steering element with built-indetector and a feedback circuit for the input beam steering elementaccording to an embodiment of the present invention and also includingan exemplary feedback control circuit for the output beam steeringelement;

FIG. 3 is a high-level flow chart of a process for manufacturing anembodiment of a beam steering element used in the switching system ofFIG. 2;

FIG. 4 is a flow chart of a process for manufacturing another embodimentof the beam steering element;

FIG. 5A is a top view of a square area of semiconductor material used tomanufacture an embodiment of the beam steering element;

FIG. 5B is a top view of the semiconductor material of FIG. 5A havingmasking material (e.g., photoresist) on its surface arranged accordingto a first pattern;

FIG. 5C is a cross-sectional view of the semiconductor material of FIG.5B after ion implantation forming an optical detector;

FIG. 5D is a top view of the semiconductor material of FIG. 5C havingmasking material on its surface arranged according to a second pattern;

FIG. 5E is a cross-sectional view of the semiconductor material of FIG.5D;

FIG. 5F is a cross-sectional view of the semiconductor material of FIG.5D after metal deposition;

FIG. 5G is a top view of the semiconductor material of FIG. 5F havingmasking material on its surface arranged according to a third pattern;

FIG. 5H is a top view of the semiconductor material of FIG. 5G after anetching process;

FIG. 5I is a top view of the reflective surface gimbal of the opticalbeam steering element of FIG. 5H;

FIG. 6A is a side view of an embodiment of a beam steering element inoperation, according to an embodiment of the present invention;

FIG. 6B is a side view of another embodiment of a beam steering elementin operation;

FIG. 6C is a side view of another embodiment of a beam steering elementin operation;

FIG. 7A-1 is a top view of a portion of an optical beam steering elementhaving four detector elements and showing a misaligned optical beam;

FIG. 7A-2 is a graph indicating the misalignment of the optical beam ofFIG. 7A-1;

FIG. 7B-1 is a top view of a portion of the optical beam steeringelement of FIG. 7A-1 showing an aligned optical beam; and

FIG. 7B-2 is a graph indicating the alignment of the optical beam ofFIG. 7B-1.

DETAILED DESCRIPTION OF THE INVENTION

A description of example embodiments of the invention follows.

FIG. 1 is a block diagram of an optical cross-connect switching system100 that may employ embodiments of the present invention. The opticalcross-connect switching system 100 includes an optical cross-connectswitch 150 (also referred to as a switch fabric) interfacing with anarray of input fibers 102 a, . . . , 102 n and an array of output fibers112 a, . . . , 112 n. In the example embodiment, each of the inputfibers 102 a, . . . , 102 n has a respective coupler 103 a, . . . , 103n that allows additional light sources (not shown) to be added to theinput fibers 102 a, . . . , 102 n. The additional light sources mayinclude light sources used for angle detection and control of beamsteering elements (not shown), as described in reference to FIGS. 2A and2B. Continuing to refer to FIG. 1, the array of input fibers 102 a, . .. , 102 n interfaces with the optical cross-connect switch 150 through acorresponding array of input apertures (e.g., lenses) 104 a, . . . , 104n and input free space interconnects 106 a, . . . , 106 n. The array ofoutput fibers 112 a, . . . , 112 n interfaces with the opticalcross-connect switch 150 through a corresponding array of outputapertures 114 a, . . . , 114 n and output free space interconnects 116a, . . . , 116 n.

The optical cross-connect switch 150 reroutes optical signals from thearray of input fibers 102 a, . . . , 102 n to the array of output fibers112 a, . . . , 112 n. Optical cross-connects (OXCs), such as the opticalcross-connect switch 150, perform switching operations in networks, suchas ring and mesh networks, to transfer information between or amongcommunicating nodes in the network, such as end user nodes, centraloffices, content servers, end user nodes, and so forth. Opticalcross-connects enable network service providers to switch high-speedoptical signals efficiently.

Conventional optical cross-connects perform switching electrically.However, as understood in the art, the combination of optical datatransmission and electronic switching requires numerousoptical-to-electrical-to-optical conversions. Electronic switchestypically convert the optical signals received on the input fiberchannels 102 a, . . . , 102 n into electrical signals, electricallyroute these signals, convert the electrical signals back into opticalsignals, and launch them into the output fiber channels 112 a, . . . ,112 n. These conversions create significant overhead in terms of powerconsumption, bandwidth limitations, size of system components, overallsystem throughput, and latency.

Electronic switches are often blocking (i.e., disallowing signal fan-outand fan-in) and are non-transparent (i.e., the signal does not stay inoptical form, and the signal may depend upon bit rate, format, andcoding). Also, in the electronic switching case, the bandwidth of theoptical signal must be within the bandwidth of the electronic switch,which can be orders of magnitude less than the bandwidth of the opticalsignal. Thus, the electronic switch becomes the network system'sbottleneck. As such, much research has been performed to developall-optical cross-connect switching systems using various mechanisms,such as movable mirrors, movable fibers, acousto-optic diffraction,electro-optic refraction, magneto-optic switching, movable bubbles, andliquid crystal addressable arrays.

FIG. 2A is a block diagram of an all-optical cross-connect switchingsystem 200, according to an embodiment of the present invention, thatprovides increased cost-effectiveness, increased reliability, anddecreased delay. An optical switch 250 according to an embodiment of thepresent invention includes (i) an input beam steering element 208 a thathas a reflective surface, such as a mirror or multi-layer dielectric,corresponding to an input fiber 202 a and (ii) an output beam steeringelement 218 n with an optical detector corresponding to an output fiber212 n. The other input fibers 202 b, . . . , 202 n and other outputfibers 212 a, . . . , 212 m also have corresponding input and outputbeam steering elements, respectively (not shown).

The optical switch 260 according to an embodiment of the presentinvention further includes a power detector 219 n, such as defined byone or more optical detector elements (details not shown), associatedwith the output beam steering element 218 n. The term “associated with”is defined herein to encompass any physical arrangement the opticaldetector element(s) can have with the reflective surface, such ascovered by, interspacially covered by, covered by a portion of, adjacentto, on top of, inset in, and so forth. The power detector 219 n detectsa position of the optical beam 205 on the surface of the beam steeringelement 218 n. The detected position is transmitted to an anglecontroller 209, which provides actuation signals to the input beamsteering element 208 a to adjust the position of the optical beam 205 onthe surface of the output beam steering element 218 n.

Couplers 203 a-n may be employed to couple light sources (not shown)with alignment wavelength(s) λa other than traffic wavelength λt (e.g.,1310 nm, 1490 nm, 1550 nm) to be presented to the input beam steeringelement 208 a and detected by the power detector 219 n. In oneembodiment, the power detector 219 n receives both the alignmentwavelength(s) λa and traffic wavelengths λt but responds (i.e., providesa signal 231) only or substantially as a function of the alignmentwavelength(s) λa. In other embodiments, the traffic and alignmentwavelengths can be positionally offset or semi-overlapping. In whicheverembodiment, an optical wavelength can be used that directly measures anangle between the input and output beam steering elements 208 a, 218 n.Details are presented in reference to FIGS. 6A through 6C and 7A and 7B.

FIG. 2B is a block diagram of an all-optical cross-connect switchingsystem 260 that includes the power detector 219 n and angle controller209 and further incorporates feedback control system 229 to control theoutput beam steering element 218 n to direct the optical beam 205 ontothe center of the corresponding output aperture 214 n. The feedbackcontrol system 229 depicted in FIG. 2B incorporates an optical powerdetector 222 n coupled to a corresponding output fiber 212 n. Theoptical power detector 222 n transmits detected power as a signal 232that is substantially a function of traffic wavelength(s) λt to signaldetection circuitry 224 n. The signal detection circuitry 224 ntransmits information about the power level to optimization feedbackcircuitry 226 n, which calculates a direction in which to orient theoutput beam steering element 218 n to optimize the optical power on theoutput fiber 212 n. The optimization feedback circuitry 226 n transmitsthe calculated direction to beam steering element driver circuitry 228n, which converts the calculated direction into a control signal 230.The control signal 230 is sent to the output beam steering element 218n, causing the output beam steering element 218 n to move and redirectthe optical beam 205 toward the center of the output aperture 214 n. Itshould be understood that a separate control system 229 may be providedto control each of the output beam steering elements 218 a-n (others notshown for clarity).

The all-optical cross-connect switching system 200, shown in FIGS. 2Aand 2B, employs free space interconnects (e.g., 206 a and 216 n) anduses two two-degree of freedom (e.g., tip and tilt axes) beam steeringelements because of spatial and angular requirements for coupling anoptical beam 205 into output apertures 214 a, . . . , 214 n. Thus, insome embodiments, the all-optical cross-connect switching system 200 isa “free-space” system, as opposed to a guided beam, solid state system(i.e., an optical cross-connect switching system employing an electronicswitch). In other embodiments, the system 200 may include guided beam,solid state elements. Other beam steering configurations are alsopossible, such as four one-degree of freedom beam steering elements. Theall-optical cross-connect switching system's 200 inputs and outputs maybe arranged in a two-dimensional array (not shown) in order to achieveeconomy of space. Thus, to direct the optical beam 205 from a particularinput fiber (e.g., 202 a) to a particular output fiber (e.g., 212 n),the optical beam 205 may be moved in two dimensions. To do so, forexample, the input beam steering element 208 a may provide beam steeringin two perpendicular directions. Similarly, and depending on the exactnature of the beam steering mechanism, the output beam steering element218 a may also provide two-dimensional beam steering capability. Forexample, if the apertures are fixed and the switch mechanism providessteering of the beam (as depicted in FIGS. 2A and 2B), the output beamsteering element 218 n may be used to ensure that an output beam 217 nis positioned optimally in the output aperture 214 n.

In the embodiment shown in FIG. 2B, the input beam steering element 208a points an input beam 207 a to the desired row and column position onthe output beam steering element 218 n. The input beam steering element208 a may position the input beam 207 a in the center of the output beamsteering element 218 n. The output beam steering element 218 n may thenrealign the optical beam 205 to the output aperture 214 n. The outputbeam steering element 218 n may direct the optical beam 205 to thecenter of the output aperture 214 n. Each input fiber 202 a, . . . , 202n and output fiber 214 a, . . . , 214 n may use dedicated beam steeringelements with two-dimensional beam steering capability. Otherembodiments may use four, single-axis, tiltable, beam steering elementsinstead of two, double-axis, tiltable, beam steering elements. It shouldbe understood that any geometric or coordinate system designs may beemployed in other embodiments, optionally in combination with the onesspecifically set forth herein.

When a connection is first established, the input and output beamsteering elements 208 a, 218 n (or at least two input and at least twooutput beam steering elements) may be tilted to prescribed tilt angles.These angles and the corresponding deflection drive signals (e.g.,voltages for electrostatically deflected beam steering elements) may bedetermined for each connection (e.g., input fiber 202 a and each ofoutput fibers 214 a, . . . , 214 n) and may be stored in system memoryand recalled when the connection is first established. The stored drivesignals, however, may result in tilt angles that are in the vicinity ofthe desired tilt angles, but are offset by some value due to drift,aging, environmental effects, etc. Thus, the system 200 may optimize thecoupling efficiency (i.e., ratio of output power to input power) with ascanning/search and an optimization method.

An example optimization method may scan the input and output beamsteering elements 208 a, 218 n incrementally until an optimum oracceptable coupling efficiency is achieved. The size of the tiltincrements (degrees) of the scan and, thus, the tilt angle drive signalincrements (e.g., voltage), may be small enough so that severalincrements result in an acceptable coupling efficiency, i.e., severalscan positions of the input and output beam steering elements 208 a, 218n may result in an acceptable coupling efficiency. In this case, thesystem is said to be less sensitive to tilt angle error. If there arefewer tilt angle increments that result in acceptable couplingefficiency, then the system is said to be more sensitive to tilt angleerror. The range of the scan may be determined by a maximum error in theangular position. The number of scan increments is the range divided bythe increment size. Thus, each scanning axis has a scanning capabilityof n positions, where n is equal to or greater than the scan rangedivided by the increment size. The input beam steering element 208 a maybe scanned through its n² positions for each position of the output beamsteering element 218 n. In such a case, there are n⁴ positions for theentire scanning range (all four tilt axes=n×n×n×n). Clever optimizationalgorithms have been developed (e.g., the hill-climbing algorithm or therosette pattern) to ease scanning time required to achieve acceptablecoupling efficiency. Nevertheless, the amount of continual processingthat may be required to establish and maintain multiple connections is achallenging aspect of free-space optical cross-connect switches.Embodiments of the present invention dramatically ease the processingrequirements and may be used in conjunction with the clever optimizationalgorithms.

Through use of an embodiment of the present invention, the number ofscan positions may be reduced from n⁴ to 2n². For instance, if the“spot” position error were 0.1 mm and the scan increment were 0.002 mm,then n=50, for which n⁴=6.25×10⁶, whereas 2n²=5000. In other words, anembodiment of the present invention may reduce the total requiredscanning positions and total scanning time in this example by as much asa factor of 1250.

This reduction may be accomplished by separating optical beam alignmentinto two stages. The first stage may include positioning the input beam206 a in the center of the output beam steering element 218 n. Thisfirst alignment stage may use one set of two-dimensional scans for whichthe total scan field is n×n=n². The second stage may include positioningthe output beam (with the output beam steering element 218 n) in thecenter of the output aperture 214 n. This second alignment stage may useone set of two-dimensional scans for which the total scan field isn×n=n².

In practice, positioning the input beam 207 a on the output beamsteering element 218 n may be less sensitive than positioning the outputbeam 217 n on the output aperture 214 n. This means that the input scanfield, n_(input) ², may be much smaller than the output scan field,n_(output) ². Without the two stage alignment process, both scan fieldsmay be restricted to the sensitivity of the output aperture 214 n. Thus,the required scan field with the invention is n_(input) ²+n_(output)²<2n_(output) ²<<n⁴. It should be understood that in alternativeembodiments or other configurations of the switching system 200, morethan two stages of scanning may be performed.

This scan field reduction (from n⁴ to 2n²) may be accomplished byconfiguring an optical detector (not shown here, but shown in FIGS.5A-5H) in the output beam steering element 218 n. This optical detectormay provide a measured signal to an angle controller 209 for output beamplacement optimization on the output beam steering element 218 n. Thetotal number of scan positions required for output beam placementoptimization is n²−n for each input beam steering element 208 a axis. Afiber power tap detector 222 n in the output fiber 212 n, which is usedin a conventional optical cross-connect set-up, is used for aligning theoutput beam steering element 218 n to the output fiber 212 n through afeedback circuit. The output beam steering element 218 n is movedthrough n positions in each of the two degrees of freedom (two axes) sothat there are n² positions for output beam 216 n alignment. Thus, thetotal scan field is 2n².

Continuing to refer to FIG. 2B, proper alignment of the output beam 217n to the output aperture 214 n results in the maximum coupling of theinput signal power to the output fiber 212 n. In practical operations,however, there is an acceptable range of coupling efficiency. Eachconnection is preferably established and maintained within thisacceptable range. Proper alignment of the output beam 217 n to theoutput aperture 214 n may be achieved through use of the feedbackcontrol system 229.

In the embodiment of FIG. 2B, the feedback control system 229 in furtherdetail includes a fiber power tap 222 n placed on the output fiber 212n. The fiber power tap 222 n may be a 1% power tap. The fiber power tap222 n connects to signal detection circuitry 224 n, which detects anoutput signal power level on the output fiber 212 n of the trafficwavelength(s) λt. The signal detection circuitry 224 n provides theoutput signal power level reading to optimization feedback circuitry 226n. Based on the output signal power level reading, the optimizationfeedback circuitry 226 n determines how to adjust the angle of theoutput beam steering element 218 n to cause the output beam 217 n toconverge into proper alignment with the output aperture 214 n. In thisembodiment, beam steering element driver circuitry 228 n provides anappropriate deflection drive signal to the output beam steering element218 n to cause it to tilt to the desired angle, as determined by theoptimization feedback circuitry 226.

The signal detection circuitry 224 n may also detect other opticaloutput signal characteristics to determine the alignment of the opticaloutput beam with the output aperture 214 n. For example, the signaldetection circuitry 224 n may be configured to detect a modulation onthe optical output signal. Modulation may be applied to wavelengths(i.e., optical signals) for use in confirming by a cross-connect switchthat the switch correctly steered the wavelength or multiple wavelengthsto the correct fiber(s).

It should be understood that the signal detection circuitry 224 n, theoptimization feedback circuitry 226 n, or the beam steering circuitry228 n may be, in whole or in part, software executing on a processor,field programmable gate array (FPGA), or other electronic device.Moreover, though represented as discrete components, the feedbackcircuits 224 n, 226 n, and 228 n may be implemented in a single circuit,a combination of circuit and software, or any other mechanism suitablefor accomplishing the functions described herein.

In one embodiment, an optical detector 219 n is configured in at leastone of the beam steering elements. In one embodiment, this element ismade from a material, such as InGaAsP, which can absorb light from anoptical signal at a traffic wavelength λt. In this embodiment, themirrors in the beam steering element 218 a-n may be designed such thatsome of the light is available for detection (see description of FIGS.6A-6C below), which provides a cost savings and performance improvementover systems with monitoring detectors external from the beam steeringelement(s).

In another embodiment, the beam steering element 218 a-n may be amaterial, such as silicon, that is transparent to the optical signalsused for telecommunications (i.e., traffic wavelength(s) λt).Semiconductors absorb and can therefore be used as detectors for lightwith wavelengths less than a cutoff wavelength. For example, silicon hasa cutoff wavelength of light at 1.1 micrometers, where typicaltransmission wavelengths used in telecommunications networks are greaterthan or equal to 1.3 micrometers. To effectively use a beam steeringelement with a silicon detector, light (i.e., the alignment wavelengthλa) is added in the couplers 103 a, . . . , 103 n (FIG. 1) or 203 a, . .. , 203 n (FIGS. 2A and 2B) at a wavelength less than the cutoffwavelength of the material used to fabricate the beam steering element.Laser sources are readily available, such as lasers at 0.980micrometers, and can be used in this manner.

The second embodiment has several advantages. First, none of the lightfrom the telecommunications signals λt passing through the device isused for alignment, minimizing losses of optical signal power of trafficwavelength(s). Excessive losses can require the need for furtheramplification of the telecommunications signals and add extra cost to anetwork. Second, incorporating the detector 219 n into the beam steeringelement 218 n as opposed to a separate element (not shown) results in acost savings and ensures optical alignment of mirrors (not shown) on theoutput beam steering elements 208 a-n relative to the detectors. Third,the use of silicon for a detector, and the fabrication of such devices,is well known and cost effective. Finally, any added cost caused byadding the extra light generating elements, such as an alignment laseroperating at 0.980 micrometers, can be reduced or minimized by sharing asingle source among all the input couplers, 103 a, . . . , 103 n(FIG. 1) or 203 a, . . . , 203 n (FIGS. 2A and 2B).

FIG. 3 is a flow chart of a process for manufacturing or fabricating abeam steering element having an integral detector. The process 300starts at step 301. In step 311, an optical detector is configured ofsemiconductor material. The American Heritage® Dictionary of the EnglishLanguage, Fourth Edition, defines the term configure as follows: “Todesign, arrange, set up, or shape with a view to specific applicationsor uses.” In step 321, a reflective surface is associated with thesemiconductor material. Finally, in step 341, a portion of thesemiconductor material is configured to be a movable beam steeringelement. The process 300 returns 303 to step 311 to manufacture anotheroptical beam steering element.

FIG. 4 is a flow chart of a process for manufacturing the same oranother embodiment of the beam steering element. The process 400 startsat step 401. In step 411, a first mask defining a p-doped region isformed on a semiconductor material, such as a silicon wafer, havingn-doped regions. In step 415, the masked semiconductor materialundergoes ion implantation to form the p-doped region. In step 421, asecond mask is formed on the semiconductor material to define areflective surface and electrical contacts. In step 437, the maskedsemiconductor material undergoes metal deposition to form the reflectivesurface and the electrical contacts that support connection of then-doped and p-doped regions to an electrical circuit. In step 441, athird mask is formed on the semiconductor material to define a gimbalframe and a reflective surface gimbal. Finally, in step 443, the maskedsemiconductor material undergoes an etching process to form the gimbalframe (e.g., X-axis gimbal) and the reflective surface gimbal (e.g.,Y-axis gimbal). The process 400 then returns 403 to step 411 tomanufacture another optical beam steering element.

FIGS. 5A through 5H referred to below further illustrate the process ofmanufacturing an embodiment of the beam steering element as set forth bythe flow chart of FIG. 4.

FIG. 5A is a top view of a square area of semiconductor material 500used to manufacture an embodiment of the beam steering element. Thesemiconductor material may be a silicon wafer or any other type ofsemiconductor material (e.g., gallium arsenide (GaAs)) of any shape orsize.

FIG. 5B is a top view of the semiconductor material of FIG. 5A havingmasking material (e.g., photoresist) 510 a on its surface arrangedaccording to a first pattern. The masking material 511 may be applied tothe semiconductor material 513 (which is ion implanted beforehand toform an N-doped region) using known photolithography techniques.Specifically, a layer of photoresist may be applied to the surface ofthe N-doped semiconductor material. The layer of photoresist may then beexposed to light, such as ultraviolet light, to selectively harden thephotoresist in specific places to form the desired pattern shown in FIG.5B. According to known photolithography techniques, either “positive” or“negative” types of photoresist may be used. In this case, negativephotoresist is used.

FIG. 5C is a cross-sectional view of the masked semiconductor materialof FIG. 5B after ion implantation 510 b forming an optical detector. Asshown, a P-doped region 515 is formed adjacent to the N-doped region 513in those areas where the hardened masking material (i.e., photoresist)is absent. In another embodiment, the optical detector may be positionedon the semiconductor material by known techniques. Multiple opticaldetectors separated by gaps may also be configured of the semiconductormaterial. Multiple optical detectors may be isolated on thesemiconductor material so that a set of reference signals are used toaccurately position the optical beam for optimum positioning.

FIG. 5D is a top view of the semiconductor material of FIG. 5C havingmasking material on its surface arranged according to a second pattern520 a. As shown, the unmasked portions of the semiconductor materialdefine a reflective surface 523 and a contact 525.

FIG. 5E is a cross-sectional view of the masked semiconductor material520 b of FIG. 5D. As shown, the masking material 521 exposes a portionof the P-doped region where metal may be deposited to form a contact.

FIG. 5F is a cross-sectional view of the masked semiconductor material530 of FIG. 5D after metal deposition. Metal 537 is deposited on theunmasked portions to form contacts to the N-doped region and areflective surface. The material for the reflective surface may be gold,silver or any other composition having reflective properties.

FIG. 5G is a top view of the semiconductor material of FIG. 5F havingmasking material on its surface arranged according to a third pattern540. The third pattern defines where the semiconductor material iscompletely removed 543, 545 to form a gimbal frame (by removing thesemiconductor material at the unmasked portions of the semiconductormaterial indicated by reference numeral 543) and a reflective surfacegimbal (by removing the semiconductor material at the unmasked portionsof the semiconductor material indicated by reference numeral 545).

FIG. 5H is a top view of the semiconductor material 550 of FIG. 5G afteran etching process. The areas indicated by reference numeral 583 havehad the semiconductor material completely removed to form a gimbal frame572 movable about torsion hinges 570 a and 570 b. The torsion hinges 570a, 570 b form a vertical axis about which the gimbal frame 572 rotatesor twists. The areas indicated by reference numeral 585 have had thesemiconductor material removed to form the reflective surface gimbal,which is movable about torsion hinges 574 a and 574 b. The torsionhinges 574 a, 574 b form a horizontal axis about which the reflectivesurface gimbal twists. In this embodiment only a part of thesemiconductor material is configured to be a movable beam steeringelement. However, in other embodiments, the entire beam steering elementmay be configured to be movable.

The n-electrode 557 and the p-electrode 555 of the p-n diode detectorare coupled to outside electronics (not shown) through a p-electrodemetallization interconnect 559 a and an n-electrode metallizationinterconnect 559 b, respectively. The p-n diode detector may be operatedin a conventional back-biased manner for improved sensitivity foroptical-to-electrical conversion.

FIG. 5I is a top view of the reflective surface gimbal 560 of FIG. 5H.The reflective surface gimbal 560 includes a reflective surface 565surrounded by the detector region 565. Again, the reflective surfacegimbal “twists” about torsion hinges 576 a and 576 b.

FIG. 6A is a side view of an embodiment of a beam steering element 600in operation according to the principles of the present invention. Thereflective surface 607 is patterned on the beam steering element tocover the center of the detector region defined by the p-doped region605. Thus, impinging light 690 may be detected at uncovered detectorregion(s) 608 a, 608 b and provide a signal through a p-electrodecontact 609 a and an n-electrode contact 609 b. This embodiment applieswhere the detector 608 a,b is made from a material that detects thetelecommunications signal and also applies where the detector 608 a,b ismade of a material that detects an added alignment signal. In each case,the beam spot size may be larger than the mirror size to ensure that thedetector 608 a,b receives adequate optical power.

FIG. 6B is a side view of another embodiment of a beam steering elementin operation 610. Reflective surfaces 617 a, 617 b, . . . , 617 n arepatterned on the beam steering element 610 in a manner allowingimpinging light 692 to be detected at gaps 616 a, 616 b between thereflective surfaces 617 a, 617 b, . . . , 617 n. Again, the diodedetector of the beam steering element includes a p-doped region 615 witha corresponding p-electrode contact 619 a and an n-doped region 613 witha corresponding n-electrode contact 619 b. This embodiment applies wherethe detector 616 a,b is made from a material that detects thetelecommunication signal and also where the detector 616 a,b is made ofa material that detects an added alignment signal. In each case, thebeam spot size should be large enough to ensure the detector 616 a,breceives adequate optical power.

FIG. 6C is a side view of another embodiment of a beam steering elementin operation 620. In this embodiment, the reflective surface 627 ispatterned on the beam steering element 620 to cover the entire detector624 formed of a p-doped region 625 and a n-doped region 623. In thisembodiment, the reflective surface 627, however, is thin enough (i.e.,transmits enough optical energy) to allow impinging light 694 to bedetected by the detector 624. This embodiment applies where the detector625, 623 is made from a material that detects the telecommunicationssignal (λt) and also applies where the detector is made of a materialthat detects an added alignment signal (λa). In each case, the intensityof the optical beam must be great enough for the detector to receiveadequate optical power through the reflective surface 627.

FIG. 7A-1 shows an embodiment of an optical beam steering element 700 ahaving four pads or contacts 709 a, 709 b, 709 c, and 709 d, each ofwhich is coupled to a respective optical detector element (not shown). Areflective surface (not shown) may be located in the center of theoptical beam steering element 700 a. The detector region surrounding thereflective surface may be opto-electrically divided by insulators orgaps 710 into four regions or quadrants (marked generally by numerals1-4) corresponding to the four detectors elements (not shown).

An optical communications signal beam 701 (i.e., traffic wavelength λt)and optical alignment beam 702 (i.e., alignment wavelength λa) are shownby way of circles superimposed on the beam steering element 700 a.

FIG. 7A-2 is a graph 705 a of output detector element signals from thefour quadrants 1-4 of optical detector elements that can be used todetermine a position of the optical signal beam 701 on the optical beamsteering element 700 a. When the optical signal beam 701 departs fromthe reflective surface, optionally in unison with an optical alignmentbeam 702 with a larger diameter than the optical signal beam 701, theoutput detector signals can be used to determine a position of the beam701 on the optical beam steering element 700 a. In this instance, thedifferent output detector signal levels from each of the detectors,caused by reaction of the detectors to the traffic or alignmentwavelength(s) λt, λa, corresponding to the contacts 709 a-d (i) indicatethat each of the detectors is exposed to unequal portions of an opticalalignment beam 702 and (ii) indicate a misaligned, optical, signal beam701, which is oriented in the center of the optical alignment beam 702.As described above in reference to FIGS. 2A and 2B, the output detectorsignals may be provided to the angle controller 209 for optimizingoutput beam placement on the optical beam steering element 700 a.

FIG. 7B-1 is a top view of a portion of the optical beam steeringelement of FIG. 7B. In this instance, equal output detector elementsignal levels from each of the detector elements (i) shows that each ofthe detector element regions are exposed to equal portions of an opticalalignment beam 702 (or optical communications beam 701 in otherembodiments) and (ii) indicates an aligned optical signal beam 701.Thus, the output detector element signals may be used to position thecenter of the optical signal beam 701 and achieve optimum alignment.

FIG. 7B-2 is a graph 705 b indicating the correct alignment by way ofequal signals produced by each of the optical detectors corresponding tocontacts 709 a-d.

It should be appreciated that the present invention can be implementedin numerous ways, including as a process, an apparatus, a system, adevice, a method, or a computer readable medium such as a computerreadable storage medium or a computer network wherein programinstructions are sent over optical or electronic communication lines.

The tilt range for a typical MEMS beam steering element is six to eightdegrees, resulting in a beam deflection angle range of twelve to sixteendegrees. Typical voltage range for a MEMS element is 40 volts. The spotalignment range (circular) to a collimated fiber is typically 10 micronsto achieve an acceptable power coupling range of −3 dB (3 dB down frommaximum coupling). An optical alignment path may be 10 cm to 1 meter.The −3 dB angular alignment range is then 0.01 to 0.1 milliradians. Thevoltage increment, assuming a linear relationship, is approximately 3millivolts. There are, thus, 104 or 214 increments in the full tiltrange of the MEMS element. There are four such tilt ranges −4×214 or 216requiring a 16-bit processor to control the voltage to the accuracyrequired throughout the range.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

It should be understood that embodiments of the optical detector mayinclude a quadrature optical detector or a detector with one, two,three, or more than four optical detector elements.

It should be understood that embodiments of the optical beam steeringelement and system may also be employed in applications of spectralregions outside of the visible optical spectrum, such as: infrared,x-ray, ultraviolet, and so forth.

It should also be understood that software used to control beam steeringelements may be stored in a computer-readable medium, such as a CD-ROMor computer memory, and loaded/executed by a digital processorconfigured to execute the software in a manner adapted to interfacedirectly or via other electronics causing the beam steering elements tosteer a beam and detect optical energy with the optical detector asdescribed herein.

It should also be understood that the optical detector described hereinmay be any known optical detector, such as a metal-semiconductor-metal(MSM) photodetector or an avalanche photodiode (APD).

1. An optical cross-connect switching system, comprising: a first beamsteering element with a reflective surface in optical association with afirst optical fiber array; a second beam steering element with areflective surface on a substrate in optical association with a secondoptical fiber array, the second beam steering element optically arrangedwith the first beam steering element to direct an optical beam from afirst optical fiber in the first optical fiber array to a second opticalfiber in the second optical fiber array; and the substrate sensitive toan alignment beam to provide information about an angle of the firstbeam steering element.
 2. The optical cross connect switching systemaccording to claim 1 wherein the substrate is a p-n diode opticaldetector.
 3. The optical cross-connect switching system according toclaim 2 wherein the p-n diode optical detector includes multiple regionsseparated by insulator gaps.
 4. The optical cross-connect switchingsystem according to claim 2 wherein the second beam steering elementincludes a reflective surface covering at least a portion of the p-ndiode optical detector.
 5. The optical cross-connect switching systemaccording to claim 1 wherein the reflective surface is on the substrateof the second beam steering element in a manner selected from a groupconsisting of: the substrate is covered by the reflective surface of thesecond beam steering element; the reflective surface of the second beamsteering element is covered by the substrate; the substrate isinterspatially covered by the reflective surface of the second beamsteering element; the reflective surface of the second beam steeringelement is interspatially covered by the substrate; the substrate iscovered by a portion of the reflective surface of the second beamsteering element; the reflective surface of the second beam steeringelement is covered by a portion of the substrate; the substrate isadjacent to the reflective surface of the second beam steering element;the substrate is on top of the reflective surface of the second beamsteering element; and the substrate is inset in the reflective surfaceof the second beam steering element.
 6. The optical cross connectswitching system according to claim 1 further comprising a controllercoupled to the substrate that controls the angle of the first beamsteering element.
 7. The optical cross-connect switching systemaccording to claim 1 wherein the first and second beam steering elementsare microelectro-mechanical system (MEMS) beam steering elements.
 8. Theoptical cross-connect switching system according to claim 1 wherein thefirst and second beam steering elements comprise two, single-axis, beamsteering elements.
 9. The optical cross-connect switching systemaccording to claim 1 wherein the first and second beam steering elementscomprise a reflective surface formed by a material selected from a groupconsisting of at least one of the following: metal or dielectric. 10.The optical cross connect switching system according to claim 1 furthercomprising a second optical detector associated with the second opticalfiber, the second optical detector adapted to provide information aboutan angle of the second beam steering element.
 11. The optical crossconnect switching system according to claim 10 further comprising acontroller coupled to the second optical detector that controls theangle of the second beam steering element.
 12. The optical cross connectswitching system according to claim 1 wherein the first and second beamsteering elements are among respective arrays of first and second beamsteering elements configured to direct optical beams from optical fibersin the first optical fiber array to optical fibers in the second opticalfiber array.
 13. The optical cross connect switching system according toclaim 1 wherein the first and second optical fiber arrays aremulti-dimensional arrays.
 14. The optical cross-connect switching systemaccording to claim 1 wherein the reflective surface of the second beamsteering element and the substrate are pivotally mounted to a frame onat least one axis.
 15. The optical cross-connect switching systemaccording to claim 14 wherein the reflective surface of the second beamsteering element and the substrate are pivotally mounted to the frame ontwo axes, the first axis orthogonal to the second axis.
 16. The opticalcross-connect switching system according to claim 14 wherein the powerdetector is electrically coupled, via the frame, to an angle controllerof the first beam steering element.
 17. An optical cross-connectswitching system comprising: an optical coupler to couple an alignmentoptical beam to a first optical path supporting a communications opticalbeam among first multiple optical paths; a first beam steering elementwith a reflective surface in optical association with the first multipleoptical paths, including the first optical path; a second beam steeringelement with a reflective surface on a substrate in optical associationwith the first beam steering element and second multiple optical paths,the second beam steering element optically arranged with the first beamsteering element to direct an optical beam from the first optical pathin the first multiple optical paths to a second optical fiber in thesecond optical path in the second multiple optical paths; and thesubstrate sensitive to the alignment optical beam to provide informationabout a position of the alignment optical beam on the substrate.
 18. Theoptical cross-connect switching system of claim 17 wherein the opticalpaths are optical fiber paths.
 19. The optical cross-connect switchingsystem of claim 17 wherein the substrate provides information about aposition of the alignment optical beam on the substrate by providinginformation about an angle of the first beam steering element relativeto the reflective surface of the second beam steering element.
 20. Theoptical cross-connect switching system according to claim 17 wherein thereflective surface is on the substrate of the second beam steeringelement in at least one of the following locations: above, below,beside, and inset.
 21. The optical cross-connect switching systemaccording to claim 17 wherein the reflective surface of the second beamsteering element and the substrate are pivotally mounted to a frame onat least one axis.
 22. The optical cross-connect switching systemaccording to claim 17 wherein the reflective surface of the second beamsteering element and the substrate are pivotally mounted to a frame ontwo axes orthogonal to each other.
 23. The optical cross-connectswitching system according to claim 22 wherein the substrate iselectrically coupled, via the frame, to an angle controller of the firstbeam steering element.
 24. The optical cross-connect switching system ofclaim 17 wherein the substrate is sensitive to wavelengths below a bandof wavelengths defining the communications optical beam.